The purpose of this BRS Shared Instrument Grant proposal is to replace the Data General computers and to purchase an upgrade for the four-circle, single crystal, x-ray crystallographic system; specifically a to make it equivalent to a Siemans - Nicolet R3m/V system. This upgraded crystallographic system will greatly assist in our structural characterizations of small organic molecules with useful biological activity and also with the structural studies related to the binding of organic molecules to strands of polynucleotides. The requested crystallographic system is also utilized as a central facility for completing structural studies routinely at subambient temperatures on materials that require special treatment. We also anticipate screening macromolecules for diffraction analysis on this facility although the actual diffraction will be performed elsewhere. The ability to maintain a central crystallographic facility for routine crystallographic investigations is essential to the research of the several groups described herein. There has been a growing increase in the demand for the use of our facility yearly. Perhaps of more significance is the fact that many of the compounds on which we currently undertake structural studies are only stable at low temperatures in an inert atmosphere. The increased versatility and reliability of upgrading our instrument will significantly increase its accessibility and broaden the scope of the Department's research efforts in determining the structures of relatively small organic molecules. The most important aspect of the requested upgrade will be the increase in reliability and the corresponding decrease in downtime due to computer hardware problems with the aging Data General equipment. A group of Chemistry Department faculty will comprise the core group of main users. Limited access is provided by recommendation to other University faculty outside of the chemistry department (e.g. Dept. of Biology and Dept. of Physics) and nearby academic investigators at other institutions (e.g. Univ. of Rhode Island and Southeastern Mass. Univ.). Priority will be given to those investigators with active PHS research support, however other investigators are never excluded from participating in the use of this instrument.